I have a rod knock, what are my options?

[MrBlah]

So, I'm pretty sure I've diagnosed the problem with my L28 to be a rod knock. So, I'd like to know what my options are for repairing this? Budget isn't an issue here, nor is my ability to do a full on rebuild, but I would like to keep it as inexpensive as possible.

 

I am also open to an engine swap, as I do have a complete carb'd small block Chevy at my disposal(no trans though).

[luseboy]

That's most likely going to take a pretty involved rebuild. I say look for a good running L6 and buy it. They aren't expensive, fairly plentiful, and you could use your current trans and everything.

[BluDestiny]

If you can weld, make some mounts buy a tranny and throw in the SBC.

[jasper]

First, please explain the symptoms/noise, and

how you determined how/why this is a rod knock.

 

If indeed you have a rod knock, many times it can be

"repaired" by replacing the bearing inserts,and sometimes

cleaning up the crank,(all in car)......cheap!

 

I have done this personaly a few times.......none have come back.

 

Tell us more............

[MrBlah]

First, please explain the symptoms/noise, and

how you determined how/why this is a rod knock.

 

If indeed you have a rod knock, many times it can be

"repaired" by replacing the bearing inserts,and sometimes

cleaning up the crank,(all in car)......cheap!

 

I have done this personaly a few times.......none have come back.

 

Tell us more............

 

You ask for more? More you shall get.

 

At first, what I heard was just a repeated knocking/rattling noise coming from somewhere around 4 or 5 cylinder, below the exhaust manifold. This turned into a rhythmic rattling that went in and out. That is, rattling/knocking that rhythmically goes in and out every few seconds. Oil pressure is a bit low, so originally I thought it might be the oil pump that was making this noise, and then it dawned on me that hey, low oil pressure can cause rod knock. So, that's as far as I've gotten. I haven't had the time to pull the oil pan and actually have a look yet. I'll be able to do that on Thursday.

Edited May 8, 2012 by MrBlah

[Tony D]

"And pulling a spark plug makes the knock go away..."

[luseboy]

Definitely pull the pan. That doesn't sound like a rod knock. Check this video:

You would be hearing a knock every revolution of the crank, most likely. I could be wrong, as I'm no expert, but I don't think that sounds like a rod knock. When's the last time you changed your oil? In my mini I started having sounds that kinda sounded like a knock. I got really worried and didn't know what to do. Suddenly it dawned on me that I hadn't changed my oil when I hit 6,000 miles (synthetic oil), so I changed it and the noise went away after a few seconds, so it was most likely valvetrain noise from oil starvation. You may have a similar problem.

[Perfect240z]

Just buy another L motor and do a swap. You can drive still and also have a L series to build up for a speedy good time

[Leon]

"And pulling a spark plug makes the knock go away..."

Wink-wink, nudge-nudge...

[jasper]

If you start to take apart the engine,

without having a SOLID diagnosis, your

only course will be to visually inspect every

moving part until you locate the cause/source

of the noise.

 

If you lack the knowledge to identify the noise, it's

possible you lack the knowledge to identify the culprit

during the visual inspection. This can be tricky, assuming

you don't find an obvious/catastrophic failure.

 

Typically a rod knock is; "loud" on start up, and then decreases.

 

Responds to snapping the throttle partially open being

louder, more pronounced.

 

Holding the throttle partially open may reveal a "sweet spot"

where the noise is very pronounced.

 

Carbon on top of a piston can cause a "rod knock".

 

If the noise is present at idle, pulling a plug wire or shorting

cylinders will lessen the noise considerably.

Also appilies when rpm is at the "swwet spot".

 

sounds similar to wrist pin and or piston slap.

 

Is said to have a "double knock" type of noise.

 

A cracked flex plate can sound JUST LIKE a rod knock

(auto trans)

 

etc, etc.

 

If this beyond your ability get a professional opinion.(keep trying)

As long as you don't take the engine apart, diagnosis is probable.

 

START by removing the engine belts, to eliminate any

rotating accessory noises/possibilities.

 

Step on the clutch to eliminate the possibility

of internal transmission noises.

Edited May 8, 2012 by jasper

[HowlerMonkey]

If you have enough piston slap or part of the skirt is missing to make that kind of noise, then the piston may be tilting enough to show lower compression on that cylinder.........which is easy to check.

 

As far as inspection, I would start with the easiest things first like inspecting under the valve cover.

 

If you don't find anything there, pulling the pan is a bit labor intensive but you can check both the lower side of the pistons and the rod bearings.

[MrBlah]

Ok, so you guys were right, it was not a rod knock. It had consumed a LOT of oil, and the oil pump was dry. Well, currently, there is increased noise from the valve train. Yes, on every revolution. Could a valve adjustment be a good idea? or may the problem be worse than that?

 

So, I know there are a lot of reasons for it to be consuming oil. What are the most likely reasons though? It does smoke a small bit now as well.

[luseboy]

I hope nothing was damaged from oil starvation. The problem could still be from the oil pump, I'd open it up and make sure everything is cool in there. The most likely cause for burning oil is your valve seals. They are a PITA to change, but not horrible. Get some viton ones out of a ford (cortina, I think?) search on here, it's been talked about more times than you can imagine. Other possibilities are rings, cylinder walls, oil pan/drain plug not sealing, busted pcv valve/system, various gaskets, etc. The most likely one is valve seals. You'll have to adjust the valves when replacing the seals anyways. Other than that it could be a big problem or a little one. Have you pulled the valve cover yet to make sure you don't have a broken rocker arm, valve, valve spring, or valve spring retainer? These can break (though not likely, but hey it's easy to inspect). Also check your timing chain and cam sprocket for problems, teeth can break off, the chain can get bent or maybe get a stiff link, etc. There's a number of things that can go wrong, it's best to inspect them. I'd say buy the "How to rebuild your nissan/datsun OHC engine" book and read up on the troubleshooting section. That book is the best $12 I've ever spent.

[MrBlah]

I was thinking valve seals. I know valve guides going bad is definitely a possibility. I'll spend a bit more time with the valve cover off, see what I can find.